The present disclosure relates to systems and methods for nuclear magnetic resonance (“NMR”) or magnetic resonance imaging (“MRI”) processes. More particularly, systems and methods are described for improved magnetic resonance fingerprinting applications.
Magnetic resonance fingerprinting (“MRF”) is an technique that enables quantitative mapping of tissue or other material properties based on varied measurements, such as random or pseudorandom variations, of the subject or object. Examples of parameters that can be mapped include longitudinal relaxation time, T1; transverse relaxation time, T2; main magnetic field map, B0; and proton density, ρ. MRF is generally described in U.S. Pat. No. 8,723,518, which is herein incorporated by reference in its entirety.
The varied measurements obtained in MRF techniques are achieved by varying the acquisition parameters from one repetition time (“TR”) period to the next, which creates a time series of images with varying contrast. Examples of acquisition parameters that can be varied include flip angle, radio frequency (“RF”) pulse phase, TR, echo time (“TE”), and sampling patterns, such as by modifying one or more readout encoding gradients.
The data acquired with MRF techniques are compared with a dictionary of signal models, or templates, that have been generated for different acquisition parameters from magnetic resonance signal models, such as Bloch equation-based physics simulations. This comparison allows estimation of the desired physical parameters, such as those mentioned above. The parameters for the tissue or other material in a given voxel are estimated to be the values that provide the best signal template matching.
Often, a slice-selective, highly undersampled spiral k-space acquisition is utilized for two-dimensional MRF acquisitions. In many instances, a spiral trajectory is changed from one time point (e.g., TR period) to the next. To enable accurate parameter estimation, for each imaging slice, upwards of 1000-2000 time points are acquired with a TR that is typically about 10 milliseconds. This results in an acquisition time of around 10-20 seconds per imaging slice. To create high-resolution volumetric parameter maps with 1 mm slice thickness, approximately 120 imaging slices will have to be imaged, resulting in a total acquisition time of 20-40 minutes. This acquisition time is quite lengthy and limits the widespread clinical usage of MRF techniques.
Given the above, there remains a need for improved an MRF acquisition techniques.